The present invention relates to a processing unit and, in particular, to a central processing unit (CPU) such as a microcontroller. Microcontrollers are well known in the art, and a large variety of such devices from low end devices (e.g., a 4/8-bit controller) to high end devices (e.g., a 32-bit controller) are available. High end controllers are used in almost any kind of electronic devices, such as laser printers and hard disks or for controlling any kind of processes, for example, in automobiles, etc.
With more complex tasks to be solved, the demand for very fast, high end controllers is rising. In particular, such devices are necessary to control real time applications. In such applications, it is necessary to react very fast to external events. If such an event occurs, the content of at least a specific set of registers needs to be switched. If this context switching is faster, the reaction time of the control system is better.